Dual slot antenna device

ABSTRACT

A dual slot antenna assembly is disclosed herein and generally includes a pair of concentrically positioned and radially spaced cylindrical conductors defining a pair of circumferential slots which are longitudinally spaced one-half wavelength apart at the anticipated operating frequency of the antenna device. An electrical signal feed assembly is connected with the conductors for exciting the slots so as to provide overlaping radiation patterns emanating in the same direction.

United States Patent [1 1 Krutsinger et al.

[451 May 7,1974

[54] DUAL SLOT ANTENNA DEVICE [75] Inventors: Jack K. Krutsinger; CarlN. Bullai;

Robert E. Munson, all of Boulder, Colo.

[73] Assignee: Ball Brothers Research Corporation,

Boulder, Calif.

[22] Filed: Dec. 18, 1970 [21] Appl. No.: 99,481

[52] US. Cl 343/708, 343/769, 343/770 [51] Int. Cl. H01 13/10 [58] Fieldof Search 343/705, 708, 767, 769, 343/791, 770

[56] References Cited UNITED STATES PATENTS 2,234,234 3/1941 Cork et al343/791 3,638,224 1/1972 Bailey et al. 343/771 3,478,362 11/1969 Ricardiet a1. 343/708 2,455,224 11/1948 Buchwalter et al 343/769 2,990,5466/1961 Haas 343/705 3,475,755 10/1969 Bassen et al..... 343/7053,139,619 6/1964 Jones 343/705 3,293,645 12/1966 Farley et al.. 343/7083,394,373 7/1968 Makrancy 343/769 3,573,831 4/1971 Forbes 343/705Primary Examiner-Eli Lieberman Attorney, Agent, or Firm-Gilbert E.Alberding [5 7] ABSTRACT A dual slot antenna assembly is disclosedherein and generally includes a pair of concentrically positioned andradially spaced cylindrical conductors defining a pair ofcircumferential slots which are longitudinally spaced one-halfwavelength apart at the anticipated operating frequency of the antennadevice. An electrical signal feed assembly is connected with theconductors for exciting the. slots so as to provide overlaping radiationpatterns emanating in the same direction.

4 Claims, 7 Drawing Figures PATENTEDMAY 71974 3810.183

SHEET 1 W2 INVENTORS' CARL N. BULLAI JACK K. KRUTSlNGER ROBERT E. MUNSONFig. 6 I

BY W 0% v ATTORNEYS DUAL SLOT ANTENNA DEVICE BACKGROUND OF THEINVENTION 1. Field of the Invention This invention relates generally toantenna assem blies and more particularly to a new and improved dualslot antenna assembly.

2. Description of the Prior Art The use of antenna assemblies for bothtransmission and reception of radio signals is well known, and suchantenna assemblies have taken many diverse dimensions and/or shapes toaccomplish given objectives. Among such antennas known in the art arethose useful in conjunction with propelled vehicles including missilesand more particularly missiles which carry instrument payloads for shortterm measurements of very high altitude environment data, which data istransmitted from an antenna mounted on a missile to receiving stationson the ground, which receiving stations are often ground trackingstations. However, monitoring has been found to be difficult due tosignal nulls encountered as the vehicles assume different roll and aspect orientations.

Although the problem has been attacked in many ways, including theuse ofrefined circuitry such as automatic gain control amplifiers which haveto some effect alleviated the problem of antenna deficiencies, therestill has been a need to improve the antennas so as to develop radiationpatterns without signal lobes of varying strength. More particularly,the antenna should be characterized by an isotropic antenna radiationcoverage, that is, a pattern of constant relative power for anyorientation of the antenna. As such, the pattern coverage is thenrelatively constant regardless of the roll or aspect orientation of therocket, thereby facilitating data monitoring at a tracking station. Theavoidance of signal nulls as a characteristic of the antenna eliminatesan important deficiency that has previously caused temporary loss ofsignal information, and in the case of an unrecovered rocket, permanentloss thereof.

Although some previous attempts have been made to design antennas havingpatterns more nearly isotropic for use in rockets carrying environmentaldata sensors and associated instruments for telemetry purposes and thelike, such antennas have not completely solved the problems in all casesdue to one or more of such diverse reasons as failing to satisfy strictaerodynamic design requirements, exhibiting intolerable signalvariations in the aspect patterns (the signal pattern measured about themissile in a plane containing the missile) and/or in the roll patterns(the signal pattern measured about the missile in a plane perpendicularto the missile axis), requiring complicated and often expensivecomponents due to complex design requirements, and/or requiringexcessive time and/or material in assembly so as to make antenna coststoo high for at least some intended uses. For example, the aspect androll radiation patterns in some antennas of recent design have beenfound to fluctuate as much as 30 db from isotropic radiation, while therequired dimensions and/or costs inherent in other such antennas havemade these antennas unusable, or at least undesirable, for many intendeduses.

SUMMARY OF THE INVENTION The present invention overcomes theaforementioned disadvantages, as well as other disadvantages, byproviding an antenna which has an improved signal radiation pattern andwhich is both simple in design and economical to make. In addition, theantenna is particularly useful in airborne telemetry vehicles, whichassume many orientations relative to any given tracking station, sinceit may be easily flush-mounted to the vehicle so as to provide a lowprofile and thereby avoid any substantial increase in air drag.

As will be seen hereinafter, a preferred embodiment of the antennaassembly constructed in accordance with the present invention generallycomprises a pair of laterally spaced-apart conductive elements defininga pair of longitudinally spaced radiation slots, each of which is ofgreater length than the spacing between the conductive elements and eachof which emanates radiation therefrom, the slots being electricallyexcited by an electrical feed assembly.

The antenna, constructed in the aforedescribed manner not only exhibitsimproved radiation patterns, but also is relatively simple in design andeconomical to produce, as will become more apparent hereinafter. It

should be noted that the antenna assembly, as constructed, is similar inmany respects to the Single Slot Cavity Antenna Assembly disclosed in anapplication, by Robert E. Munson et al. Ser. No. 99,434 and filedconcurrently herewith. However, because of the dual slot feature, theantenna assembly of the present invention operates in an entirelydifferent manner as will be seen hereinafter, and may be utilized indifferent operational environments. In addition, because of this dualslot feature, assemblage of the antenna assembly of the presentinvention is different than that of the single slot antenna assemblyreferred to hereinabove.

An object of the present invention is to provide a new and improvedantenna assembly having an improved signal radiation pattern.

Another object of the present invention is to provide a new and improvedantenna assembly which is both simple in design and economical tomanufacture.

Still another object of the present invention is to provide a new andimproved antenna assembly which utilizes a pair of longitudinally spacedcircumferential slots for the emanation of radiation patterns.

Another object of the present invention is to provide an antennaassembly of the last-mentioned type wherein the electromagnetic energyemanating from the aforementioned slots radiate in the same direction soas to provide an overall radiation pattern of improved quality.

Still another object of the present invention is to provide an antennaassembly of the lastmentioned type wherein slot excitation is providedwith only one electrical signal feed assembly.

These and other objects and features of the present invention willbecome more apparent to those skilled in the art from the followingdescription of a preferred embodiment, as illustrated in theaccompanying drawmgs.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings:

FIG. 1 is a perspective view of a missile utilizing a dual slot antennaassembly constructed in accordance with the present invention;

FIG. 2 is an enlarged perspective view of the antenna assembly apartfrom the missile illustrated in FIG. 1',

FIG. 3 is a corss-sectional view taken generally along line 3-3 in FIG.2;

FIG. 4 is a partially broken-away enlarged sectional view takengenerally along line 4-4 in FIG. 3 and particularly illustrating theradiation patterns emanating from the antennas dual slots;

FIG. 5 is an enlarged flattened out view of the antenna illustrated inFIG. 2, specifically displaying a portion of the electrical signal feedassembly used therewith;

FIG. 6 is a diagrammatic view of aportion of the antenna of FIG. 2,illustrating the manner in which the dual slots operate; and

FIG. 7 is a graphic representation showing an experimental antenna gainradiation pattern utilizing the antenna of FIG. 2.

DESCRIPTION OF THE PREFERRED EMBODIMENT Turning now to the drawings,wherein like components are designated by like reference numeralsthroughout the various figures, a dual slot antenna assembly l0,constructed in accordance with the present invention, is shown in FIG. 1flush-mounted to a missile 12 having a metallic outer cylindrical bodyor skin 14 and a nose portion 15. As will be seen hereinafter, antennaassembly is characterized by an isotropic antenna radiation coverage,that is an omnidirectional dipole type pattern of constant relativepower for any orientation of the antenna. As such, the pattern coverageis then relatively constant regardless of the roll or aspect orientationof missile 12 thereby facilitating data monitoring at a trackingstation. For purposes of description, the antenna will be considered asa transmitting device, it being readily apparent to those skilled in theart that the same may be used for reception purposes also.

Turning to FIGS. 2 through 5, antenna 10 is shown to include a thininner cylindrical conductor 18, preferably constructed of copper, theconductor being adapted for flush mounting directly to and about theskin 14. of missile 12, as illustrated in FIG. 1, and thereby providing,in effect, a ground plane having an axial length equal to that of themissile. Antenna l0 further includes a thin second or outer cylindricalconductor 20, which is also preferably constructed of copper, and whichdisplays an axial length substantially equal to one-half wavelengthatthe anticipated operating frequency of the antenna. Conductor 20 ispositioned concentrically about one end portion of conductor 18 and isradially spaced therefrom so as to define a one-half wavelength coaxialcavity 22, asillustrated best in FIG. 3. In accordance with a feature ofthe present invention, cavity 22 is electrically opened at both endsthereof so as to provide a pair of exposed circumferential slots 23 and25 which are longitudinally spaced one-half wavelength apart at theantennas anticipated operating frequency and which, as will be seenhereinafter, cooperate to produce the aforestated omnidirectionalradiation pattern.

While coaxial cavity 22 may be left void of material, for ease ofconstruction a dielectric layer 24, preferably polytetrafluoro ethylene(commercially available Teflon), and particularly Teflon-fiberglass, ispositioned between and supports conductors 18 and 20. In this regard, itis to be noted that the actual length of coaxial cavity 18 must becorrected for the impedanceproducing effect of the dielectric layer.This may be accomplished by resorting to the relationship of effectivewavelength M- as a function of actual wavelength A, which relationshipis:

- dielectric material, such as material 24, an effective one-halfwavelength cavity is contemplated.

Thus, for operation at a carrier frequency of, for example, 2.2 GHZ andutilizing a dielectric such as polymerized tetrafluoro ethylene, A isapproximately equal to 5.4 inches and ER is approximately 2.5 inches.Solving the aforestated equation yields a M of approximately 3.4 inches.Therefore, the effective one-half wavelength cavity of this exampleisapproximately 1.7 inches in length with slots 23 and 25 being separatedthe same distance.

Circumferential slots 23 and 25 may be excited by signal energy producedat a source 30, as seen in FIG. 3, which may be located within missilel2 and which may be of conventional type such as, for example, a unithaving an appropriate power source and radio frequency oscillatormodulated in accordance with data signals from external environmentalsensor devices. In this regard, a single electrical signal feed assembly32, operating in the TEM'mode, is provided for coupling source 30 to theaforementioned slots, as will be seen hereinafter.

As illustrated best in FIG. 3, feed assembly 32 includes a coaxialtransmission line 34 having outer and inner conductive cables 36 and 38extending from within source 30 where they are connected to theappropriate components. The otherwise free end of outer conductive cable36 is electrically connected to inner conductor 18 while the otherwisefree end ofinner conductive cable 38 is connected to the input of acombination multiple feed and impedance-matching network 40 which ispart of assembly 32 and which is to be described hereinafter.

The connections of the inner and outer conductive cables of transmissionline 34 with conductor 18 and network 40, respectively, may beaccomplished in any of conductive cable 36, as illustrated in FIG. 3. Inthis manner, the last mentioned conductive cable is electricallyconnected to inner conductor 18 while, on the other hand, innerconductive cable 38 of coaxial transmission line 34 is positionedthrough insulating sleeve 46 and aligned aperture 48 for connection withcombination multiple feed and impedance matching network 40.

Turning to FIG. 5, attention is directed to network 40 which issupported on the exposed side of dielectric layer 24 and which comprisesa plurality of thin ribbonlike conductive leads constructed preferablyof and displaying the same thinness as outer cylindrical conductor 20.In this regard, it has been found that the most favorable radiationpatterns emanating from slots 23 and 25 of coaxial cavity 22 aredeveloped when the slots are excited in the TEM mode with a plurality ofuniform phase and amplitude signals provided at feed points generallydesignated by the reference numeral 53. As illustrated, these feedpoints are separated about the periphery of circumferential slot 25 (onouter conductor 20) at intervals substantially equal to one wavelength(as corrected for the dielectric material 24 in cavity 22) at theaforestated anticipated operating frequency. Accordingly, network 40includes a first plurality of leads 52, common ends of which arepreferably integrally formed with, but in any case, terminate at feedpoints 53.

Assembly 40 further includes a plurality of T-shaped leads 54 (two ofwhich are shown in FIG. 5), a third plurality of leads 56 and an inputlead 58, all of which combine to connect the first plurality of leads 52to the inner conductive cable 38 of coaxial transmission line 34 at asignal feed junction designated by the reference numeral 59. Asillustrated in FIG. 5, the head of each T-shaped lead connects a pair ofadjacent leads 52 while the leads 56 substantially form a continuousband connecting the base of each T-shaped lead to input lead 58. In thisregard, it is to be noted that dielectric layer 24 maintains thepredetermined orientation between the aforestated leads as well as theinner and outer conductor.

Leads 52, 54, 56 and 58 are suitably dimensioned (length, width andthickness) so as to provide continuous impedance matching betweencoaxial transmission line 34 and coaxial cavity 22. With the impedanceof coaxial transmission line 34 being appropriately chosen so as tomatch the impedance of source 30, it is readily apparent that there issubstantially a perfect impedance match between the source and antennawhich, of course, provides for a more efficient antenna. In addition,the distances between input 58 and each feed point 53 are equal. In thismanner, combination multiple feed and impedance matching network 40separates the input signal from coaxial transmission line 34 into aplurality of equal phase and amplitude signals and transfers the same tofeed points 53 for exciting slots 23 and 25 in the most favorable mannerpossible.

While network 40 is formed in the manner illustrated in FIG. 5 andincludes four paths to conductor 20, it is to be understood that theinvention, as contemplated, .is not limited thereto. For example, theremay be any number of feed points and paths depending upon thecircumference of conductor 20. Accordingly, the paths between input 58and feed points 53 may take on various dimensions and designs so long asthe aforedescribed impedance matching and input signal separationfunctions are preserved. in this regard, the latter function is assuredif the paths are of equal distances.

With antenna device 10 constructed in the aforedescribed manner,attention is now directed to a preferred method of making the same. Asstated above, inner and outer cylindrical conductors l8 and 20 arepreferably constructed of copper. More specifically, these conductorsare preferably parts of a sheet of microstrip, that is, copper-cladlayers supported by and on opposite sides of a sheet of dielectricmaterial such as, polytetrafluoro ethylene (commercially availableTeflon), the dielectric sheet being dielectric material 24 illustratedin FIG. 2.

The method of making antenna 10 utilizing the aforedescribed sheet ofmicrostrip includes the step of removing various portions of one of thecopper-claded layers from the intermediate dielectric insulating sheetso as to provide an intergral configuration including outer conductor 20and combination multiple feed and impedance matching network 40. Thismay be accomplished in any suitable manner, but is .mostpreferablyaccomplished by resorting to conventional printed circuit boardtechniques such as, for example, a photoetching process. Thereafter,aperture 48 is provided through the laminated material at the input orsignal feed junction of assembly 40 and a suitable jack assembly of thetype described above is soldered or otherwise suitably mounted over-theaperture on the opposite side of network 40,:in the manner illustratedin FIG. 3.

If the antenna assembly is to be used in the manner shown in FIG. 1,that is, as a wrap-around or cylindrical flush-mounted antenna, thelongitudinal edges of the microstrip or laminated material are suitablyconnected togetherby any suitable means such as apertures 61 providedthrough opposite sides of the material as illustrated in FIG. 5. In thisregard, construction of antenna device 10 is facilitated by connectingonly the lengthwise edges of the intermediate dielectric layer 24 asillustrated by gaps 60 and 62 representing the unconnected lengthwiseedges of inner and outer conductors 18 and 20, respectively. So long asthese gaps are small relative to the operating wavelengths of theantenna, they may be neglected as having no substantial effect on eitherthe antenna impedance or radiation pattern. In this regard, thelongitudinal edges of the laminated material may be connected togetherafter the antenna assembly is wrapped around the body of the propelledvehicle or they may be initially con nected together whereupon theassembly is then slid over and about the vehicles body.

Having described the rather simple and economical manner in whichantenna device 10 is constructed, attention is now directed to itsoperation, which may be best described in conjunction with FIG. 6illustrating a portion of the antenna assembly diagrammatically. Asstated above, circumferential slots 23 and 25 are excited in the TEMmode by a plurality of equal phase and amplitude signals (such as radiofrequency signals) which are fed to the cavity at points 53 adjacentslot 25 by electrical signal feed assembly 32. For purposes of clarity,FIG. 6 shows a single conventional coaxial cable which is connected withconductors 18 and 20 adjacent slot 25 and which, for purposes ofexplanation, represents a portion of feed assembly 32.

From an impedance standpoint, because circumferential slots 23 and 25are electrically in parallel and one-half wavelength apart, slot 25presents only onehalf of the impedance which would otherwise exist ifthe slot 23 were replaced by a short circuit. This, of course, is animportant consideration when matching the impedance of antenna 10 withthat of the electrical signal feed assembly 32. Upon exciting coaxialcavity 22, an electric field develops about slot 25 in the directionindicated by arrow E This, of course, only represents the instantaneouselectric field and will change in accordance with the oscillatorysignals exciting the cavity. Since circumferential slot 23 is positionedone-half wavelength from slot 25, the instantaneous electric fieldshifts 180 thereat, as indicated by arrow E In this manner, the electricfields at the two slots are always in opposite directions. Accordingly,the electromagnetic energy emanating from the two slots radiate in thesame direction, as indicated by arrows R and R respectively, andtherefore overlap in an additive manner so as to provide a strongerradiation pattern, as illustrated in FIG. 4.

In the case where antenna assembly 10 is utilized in combination withmissile 12, as illustrated in FIG. 1, it has been found that theantennas dual slot feature provides a typical omnidirectionaldipole-type radiation pattern, however, displaying more broadside gainand less nulls in the roll axis due to dual slot cooperation. In thisregard, it is to be noted that assembly 10 operates effectively at anydesired frequency and operates particularly well at frequencies withinthe VHF, UHF and microwave bands generally and at the aforestatedfrequency of 2.2 GHz'specifically.

Referring to FIG. 6, the aspect radiation pattern developed by antennadevice 10 utilized in the manner illustrated in FIG. 1 is shown, whereinthe axis of the missile was positioned substantially within the planecontaining the pattern and wherein the assembly was operated atafrequency of 2.2 GHZ. It is to be understood that this particularfrequency is provided for illustrative purposes only and is not intendedto limit the invention, the assembly operating equally well at otherdesired frequencies.

The pattern, representing the antenna gain relative to linear isotropicradiation, is substantially representative within one db of the infinitenumber of aspect radiation patterns which may be utilized to define afigure of revolution about the missile axis. More particularly, theradiation pattern of FIG. 7 is substantially representative of thepattern contained in any plane defining a cross section for any figureof revolution produced by all aspect patterns containing the axis of themissile.

missile I It readily may be appreciated that deep nulls exist onlydirectly forwardly and rearwardly (l80) of the missile, that is, at thetip and tail thereof. As is well known, tip and tail pattern nulls in atelemetry missile are usually of little concern. As can also be seenfrom FIG. 7, the remainder of the signal pattern displays an averagestrength variation between peaks and nulls in the aspect plane of lessthan db. Thus, the improved antenna device is highly favorable forreceipt of transmission of electromagnetic signal energy to or from themillile without any appreciable loss in the signal due ot thevehicleorientation.

It is to be understood that while antenna device 10 has been describedboth operationally and in construction as a cylindrical flushmountable-type antenna displaying an omnidirectional radiation pattern,the invention is not limited thereto. Specifically, antenna device 10may be substantially flat or only partially curved so as to provide amore directional radiation pattern while retaining the variousadvantageous features described above. In addition, although only oneembodiment of the invention has been shown and described, variousmodifications as may appear to those skilled in the art are intended tobe within the contemplation of the invention as defined in the scope ofthe claims.

What is claimed is:

l. A dual slot antenna assembly comprising: a pair of laterallyspaced-apart conductive elements electrically isolated with respect toone another, said conductive elements defining a pair of radiation slotslongitudinally spaced-apart a predetermined distance approximately equalto one-half wavelength at the anticipated operating frequency of saidassembly, each of which slots emanates radiation therefrom .such thatthe radiation patterns developed are in substantially the samedirection, said slots being of greater length than the spacing betweensaid conductive elements; and electrical signal feed means connectedwith said conductors for electrically exciting both of said slots, saidelectrical signal feed means including a plurality of leads connected toan edge of one of said conductive elements adjacent one of said slotsand spaced-apart at intervals at least substantially equal to onewavelength at said anticipated operating frequency.

2. An assembly according to claim 1 including nonconductive means forsupporting said laterally spacedapart conductive elements, saidconductive elements and nonconductive means each comprising part of asingle sheet of dielectric material metallically cladded on oppositesides thereof.

3. A dual slot antenna assembly comprising: a first substantiallycylindrical conductor, the axial length of which is approximately equalto one-half wavelength at the anticipated operating frequency of saidassembly; a second substantially cylindrical conductor, the axial lengthof which is at least equal to the axial length of said first conductor,said second conductor being positioned concentrically within andradially spaced from said first conductor and electrically isolated withrespect thereto so as to define a pair of circumferential slots spacedone-half wavelength apart at said anticipated operating frequency andproviding independent radiation patterns emanating in the samedirection;

and electrical signal feed means connected with said conductor forelectrically exciting both of said slots, said electrical signal feedmeans including a plurality of leads connected to an edge of said firstconductor adjacent one of said 'slots and circumferentially spacedapartat intervals at least substantially equal to one wavelength at saidanticipated operating frequency.

4. An assembly according to claim 3 including nonconductive means forsupporting said first and second conductors, said conductors andnonconductive means each comprising part of a single sheet of dielectricmaterial metallically cladded on opposite sides thereof.

1. A dual slot antenna assembly comprising: a pair of laterallyspaced-apart conductive elements electrically isolated with respect toone another, said conductive elements defining a pair of radiation slotslongitudinally spaced-apart a predetermined distance approximately equalto one-half wavelength at the anticipated operating frequency of saidassembly, each of which slots emanates radiation therefrom such that theradiation patterns developed are in substantially the same direction,said slots being of greater length than the spacing between saidconductive elements; and electrical signal feed means connected withsaid conductors for electrically exciting both of said slots, saidelectrical signal feed means including a plurality of leads connected toan edge of one of said conductive elements adjacent one of said slotsand spaced-apart at intervals at least substantially equal to onewavelength at said anticipated operating frequency.
 2. An assemblyaccording to claim 1 including nonconductive means for supporting saidlaterally spaced-apart conductive elements, said conductive elements andnonconductive means each comprising part of a single sheet of dielectricmaterial metallically cladded on opposite sides thereof.
 3. A dual slotantenna assembly comprising: a first substantially cylindricalconductor, the axial length of which is approximately equal to one-halfwavelength at the anticipated operating frequency of said assembly; asecond substantially cylindrical conductor, the axial length of which isat least equal to the axial length of said first conductor, said secondconductor being positioned concentrically within and radially spacedfrom said first conductor and electrically isolated with respect theretoso as to define a pair of circumferential slots spaced one-halfwavelength apart at said anticipated operating frequency and providingindependent radiation patterns emanating in the same direction; andelectrical signal feed means connected with said conductor forelectrically exciting both of said slots, said electrical signal feedmeans including a plurality of leads connected to an edge of said firstconductor adjacent one of said slots and circumferentially spaced-apartat intervals at least substantially equal to one wavelength at saidanticipated operating frequency.
 4. An assembly according to claim 3including nonconductive means for supporting said first and secondconductors, said cOnductors and nonconductive means each comprising partof a single sheet of dielectric material metallically cladded onopposite sides thereof.